BOSTON (Reuters) - Wall Street investors were so convinced that Hunter Harrison could turn around railroad CSX Corp CSX.O that the company lost $4 billion in market value when the former CEO took a medical leave in December and died only a few days later.

FILE PHOTO: A CSX freight train crosses the Potomac River in Harpers Ferry, West Virginia, U.S. on October 16, 2012. REUTERS/Gary Cameron/File Photo

But rather than run for the door, a number of prominent hedge fund managers either established new positions or added to what they already owned, certain that someone else would execute on the plans the railroader had put in place only months before.

Steadfast Capital Management, run by Robert Pitts, and Suvretta Capital Management, run by Aaron Cowen, made new bets on CSX during the last three months of 2017 while Citadel Advisors more than doubled its bet, according to regulatory filings released on Wednesday and data from Symmetric.IO.

Steadfast owned 4.5 million CSX shares on Dec. 31, marking the biggest increase in ownership from the previous quarter, the data show. Suvretta, which ended 2017 with a 24.6 percent gain, owned 2.5 million shares and Citadel, whose multistrategy fund gained roughly 13 percent last year, owned 3.3 million shares after having bought an additional 2.4 million shares during the quarter.

Chilton Investment Co added a new position to own 1.5 million shares at the end of the quarter and Sirios Capital Management bulked up its holding by 264 percent to own 1.8 million at the end of the quarter.

While it is not clear exactly when during the quarter the funds made their bets, several hedge fund managers said the price became more attractive after Harrison’s death, prompting some to buy then.

The hedge funds are relatively smaller investors, trailing powerhouses Vanguard Group, BlackRock and State Street Global Advisors, and activist investor Paul Hilal. Hilal, whose Mantle Ridge owns 42.7 million shares, was instrumental in bringing Harrison to CSX from rival Canadian Pacific last March.

But the fact they are there at all suggests confidence that CSX can benefit from the growing economy as well as the new tax plan, analysts and investors said. And it underscores that they are willing to give Harrison’s replacement, Jim Foote, who long worked with Harrison and was most recently CSX’s chief operating officer, a chance, they added.

After Harrison’s death the share price climbed roughly 12 percent in around three weeks, rewarding the newcomers.

Since then the shares have retreated as investors demand more information on how Foote will handle the turnaround plan that includes deep job cuts and rail yard closures and has triggered persistent service disruptions, customer complaints and federal scrutiny.

There were, of course, some funds that exited during the last quarter. Brahman Capital sold 4.8 million shares while OZ Management sold 3.8 million to exit their positions.

Spokespeople for the funds declined to comment.