Boston authorities are searching for another man who disappeared after a Celtics game last week, putting the city on edge after similar disappearances ended in tragedy.

Michael Kelleher was last seen at the TD Garden on Wednesday, March 29. While family and friends hang posters all over downtown, police have begun the unfortunate formality of searching the Charles River.

While they've turned up nothing, the case is raising concern about other young men who vanished only to be found in the waters around Boston.

In recent years, eleven people -- mostly men -- have gone missing and turned up weeks or months later in the water.

Some of them were found in the Charles River, while others were found in Boston Harbor. Some of the deaths were found to be accidents, others suicide.

But the sheer number of similar cases has led to questions on social media and spawned online conspiracy theories.

"The events I was involved with and the investigations I helped oversee were all unfortunate accidents," former Boston Police Chief Dan Linskey told FOX25.

He said the waters around Boston, especially Downtown Boston, present a real hazard to anyone who might be lost, disoriented, or intoxicated late at night.

Linskey said the common denominator among most of the cases is alcohol and there’s not a serial killer out there.

“No, it’s been a series of unfortunate events that have been properly investigated by Boston police. The evidence has showed unfortunate accidents have occurred,” said Linskey.

It's important to say no one knows what happened to Michael Kelleher.

If you're going out in Boston late at night, Chief Linskey advises groups stay together and make sure your friends don't go walking off alone -- especially if they've had a lot to drink.