An inmate sentenced to over 100 years for crimes including the attempted murder of police officers escaped from the parking lot of a mental hospital in Maryland after he slipped away from his handcuffs in a police van, officials said, sparking a manhunt Friday.

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David Watson escaped from the custody of the Wicomico County Sheriff's Office at Clifton T. Perkins Hospital Center in Jessup, Maryland, where an evaluation was scheduled, according to law enforcement officials. He bolted into the woods, Fox 45 reported.

Police immediately launched a manhunt with K-9 dogs and helicopters.

The 28-year-old inmate's handcuffs and waist chain turned up near the van, Howard County police spokeswoman Sherry Llewellyn said, adding that Watson had been serving his sentence in Delaware.

He's been charged with attempted murder and other offenses on Maryland'sa Eastern Shore related to shootings of police officers' homes.

Watson was described as a white male, 5-foot-8-inches tall and 140 pounds. He was wearing all-white when he escaped, Llewellyn said.

It was not clear whether his escape was planned or spontaneous, the spokeswoman added.

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The Associated Press contributed to this report.