Stocks notched their biggest one-day plunge all year on Monday, with the Dow closing down 265 points. Stocks were already down Monday as lackluster economic numbers out of China prompted investors to dump commodities, and a pair of deadly explosions at the finish line of the Boston Marathon on Monday afternoon cemented their drop. The Boston tragedy was expected to be the question on which markets would hinge Tuesday, too, according to CNBC. On Monday afternoon, all of the Dow's 30 components closed down, while the S&P fell more than 36 points and the Nasdaq lost more than 78. Just before Wall Street tanked on Monday, it had snapped a four-day winning streak Friday — but it still had closed up more than 2 percent last week. The decline in U.S. stocks began early Monday just after new data showed China's gross domestic product had grown 7.7 percent in the first quarter over the same period a year ago‚ below analysts' expectation of 8 percent and down from 7.9 percent in the previous quarter.