By Sara Sjolin, MarketWatch , Ryan Vlastelica

S&P 500, Nasdaq Composite book weekly losses, Dow ends little-changed; Shares of Amazon slump after results, offsetting Alphabet gain

U.S. stocks ended a volatile session with modest losses on Friday, pressured by the surprise announcement that the Federal Bureau of Investigation was restarting a probe (http://www.marketwatch.com/story/fbi-restarting-probe-into-hillary-clintons-emails-2016-10-28) into Hillary Clinton's emails, adding a new dose of political uncertainty into the market.

Major indexes had traded higher earlier in the session, supported by a strong GDP reading, but the news prompted a turnaround and extended the week-to-date declines of the S&P 500 and Nasdaq. However, indexes also ended well off their lows of the session as investors digested the news and its potential implications for the coming election.

The restarted probe came after FBI Director James Comey said he had learned of emails that "appear to be pertinent" to its investigation, though he added that the FBI "cannot yet assess whether or not this material may be significant." In July, Comey had said that charges against Clinton--who controversially used a private email server while secretary of state--weren't "appropriate."

See also:FBI probe into new Clinton emails hit Wall Street in 4 key ways (http://www.marketwatch.com/story/3-ways-a-fresh-fbi-probe-into-clinton-emails-hit-wall-street-2016-10-28)

Polls have strongly indicated that Hillary Clinton, the Democratic presidential candidate, will win out over Republican Donald Trump in next month's election, an outcome that analysts said markets had priced in.

"This throws such a monkey wrench into anyone's ability to predict what will happen over the next couple of weeks," said Wayne Kaufman, chief market analyst at Phoenix Financial Services. "Most people had been predicting a Clinton victory, and all of a sudden the waters are muddied again. Markets hate uncertainty more than anything else."

The Dow Jones Industrial Average slid 8.49 points, or 0.05%, to finish at 18,161.19. The S&P 500 index fell 6.63 points, or 0.3%, to close at 2,126.41. The Nasdaq Composite Index lost 25.87 points, or 0.5%, to 5,190.10.

For the week, the S&P lost 0.7% while the Nasdaq fell 1.3%. The Dow managed to eke out a weekly gain, up less than 0.1% over the past five sessions.

See also:The stock market has reached a historic level of quiet (http://www.marketwatch.com/story/the-stock-market-has-reached-a-historic-level-of-quiet-2016-10-26)

Market action on Friday was also driven by a number of high profile companies reported earnings since Thursday's close, results provided little in the way of a trend. Among energy companies, Chevron Corp(CVX) rallied while Exxon Mobil Corp.(XOM) fell, while in the tech sector, a rise in the shares of Alphabet Inc. (GOOGL), the parent company of Google, was offset by a sharp decline in Amazon.com Inc.(AMZN).

A preliminary read of third-quarter gross domestic product showed the fastest pace of expansion since mid-2014 (http://www.marketwatch.com/story/gdp-hits-29-in-biggest-gain-since-mid-2014-2016-10-28), with the economy growing 2.9%, in line with expectations. The report showed acceleration from the growth rate of 1.4% seen in the previous quarter.

The data was seen as doing little to change the view that the Federal Reserve would raise interest rates at its December meeting. The U.S. central bank has said it would raise rates when it deems the economy strong enough to withstand such a move.

The policy-setting Federal Open Market Committee meets Nov. 1-2, but expectations for a rate increase are low ahead of the Nov. 8 election. Instead, markets are pricing in a tightening at the December meeting, with the CME Group data showing an 83% probability of a hike in December.

In other data released on Friday, consumer sentiment unexpectedly dipped from the prior month, but markets didn't react much to the report.

Read:Get ready to cheer the best five days of the year for stocks (http://www.marketwatch.com/story/get-ready-to-cheer-the-best-five-days-of-the-year-for-stocks-2016-10-27)

Corporate movers: Shares of Amazon dropped 5.2% to $775.88, following disappointing earnings reported late Thursday (http://www.marketwatch.com/story/amazon-posts-smaller-than-expected-profit-increase-2016-10-27-164855144). While the e-commerce giant's revenue came in line with forecasts, earnings were below expectations.

On the upside, Google-parent Alphabet rose 0.3% to $819.56 following stronger-than-expected earnings out on Thursday (http://blogs.marketwatch.com/thetell/2016/10/27/alphabet-expected-to-report-stronger-earnings-and-sales-live-blog/).

In the energy sector, both Chevron and Exxon reported sharp drops in quarterly earnings, hurt by weak oil prices. However, Chevron rose 3.9% as it nonetheless returned to profitability (http://www.marketwatch.com/story/chevron-returns-to-profit-though-revenue-slides-2016-10-28) following three straight quarters of losses. The stock was the biggest percentage gainer among Dow components. Exxon fell 2.5% after reporting its ninth straight quarter of falling revenue (http://www.marketwatch.com/story/exxon-mobil-profit-and-revenue-slide-again-2016-10-28-84853357).

Read:This market barometer says Trump still has a chance at the White House (http://www.marketwatch.com/story/this-market-barometer-says-trump-still-has-a-chance-at-the-white-house-2016-10-28)

Among other movers, Baker Hughes Inc.(BHI) rallied 8.4% after The Wall Street Journal reported that General Electric Co.(GE) was in talks to merge its oil-and-gas business with the oil-services company (http://www.marketwatch.com/story/general-electric-said-to-explore-baker-hughes-purchase-2016-10-27).

Hershey Co.(HSY) gained 7.2% after the chocolate company reported third-quarter earnings that beat estimates (http://www.marketwatch.com/story/hershey-third-quarter-earnings-beat-estimates-2016-10-28).

Amgen Inc.(AMGN) sank 9.6% after the biotechnology company late Thursday beat third-quarter earnings expectations and raised its profit outlook, but kept its sales outlook virtually unchanged (http://www.marketwatch.com/story/amgen-beats-profit-expectations-and-raises-its-outlook-2016-10-27).

U.S.-listed shares of Sanofi SA(SAN.FR) (SAN.FR) finished up 4.3% after the French drug giant lifted its profit outlook (http://www.marketwatch.com/story/sanofi-raises-profit-outlook-after-upbeat-results-2016-10-28).

See:

Other markets: Asia markets ended mostly in the red (http://www.marketwatch.com/story/most-asian-markets-down-but-nikkei-trades-up-2016-10-27), but with Japan's Nikkei 225 bucking the trend. The Japanese index ended 0.6% higher as the yen weakened after data showed consumer prices dropped in September.

The ICE dollar index fell 0.5%, and saw heavy volatility following the news of the FBI probe into Clinton's emails.

Markets in Europe closed lower (http://www.marketwatch.com/story/european-stocks-drop-as-anheuser-busch-cuts-view-french-data-disappoint-2016-10-28).

Oil prices settled (http://www.marketwatch.com/story/oil-prices-hold-steady-ahead-of-weekend-opec-meeting-2016-10-28)2 lower%, while gold finished at its highest level since Oct. 3 (http://www.marketwatch.com/story/gold-futures-drift-lower-ahead-of-us-gdp-reading-2016-10-28).

(END) Dow Jones Newswires

October 28, 2016 16:33 ET (20:33 GMT)

Copyright (c) 2016 Dow Jones & Company, Inc.