Dzhokhar Tsarnaev, one of two suspects in the Boston Marathon bombings, is in serious condition under heavy guard at the Beth Israel Deaconess Medical Center in Boston Sunday after being apprehended in the city suburb of Watertown Friday.

Authorities believe Tsarnaev’s serious neck injury may have been caused by a failed suicide attempt, CBS News reported. Investigators think the bullet wound was not sustained during a police shootout.

Tsarnaev, 19, has not yet been charged in the case. Communication with him has been hindered because the injury has made him unable to speak.

On Thursday night, brothers Tamerlan Tsarnaev and Dzhokhar Tsarnaev engaged in a high-profile shootout with law-enforcement authorities. The former was killed, but the latter evaded police most of Friday by hiding in a boat in the backyard of a house in Watertown.

When Dzhokhar Tsarnaev was captured by police, he was seriously injured with two bullet wounds, one in the leg and another in the back of the neck. That bullet wound in the neck is particularly interesting to investigators. Based on the bullet’s exit point, investigators believe that Tsarnaev stuck a gun inside his mouth and fired in an attempt to kill himself before his capture by police.

“Of course, he and his brother were in a big shootout," CBS New correspondent John Miller said on air. "But [investigators are] saying that wound to the back of the neck is very possibly a suicide attempt. They say it appears from the wound that he might have stuck a gun in his mouth and fired, and [the bullet] actually just went out the back of his neck without killing him. That's one of the reasons he's unable to communicate, but he can understand what they're saying. And they believe there will be a point where he will be able to talk to him.”