WATERTOWN, Mass. (AP) – Police investigating the pipe bombing of a Watertown biotech business obtained an arrest warrant on Tuesday for a Framingham man charged with previously trying to blow up the same building in 2003.

Police asked for the public’s help finding the man, Brad Karger, 29. Karger will be charged with placing an explosive device and burning a building, according to Watertown police.

The pipe bomb exploded at about 3:41 a.m. last Thursday in a lab area at Amaranth Bio Inc. shattering windows but causing no injuries. Police said the building had been broken into.

On its Web site, Amaranth describes itself as an early stage biotech company whose products harness “native processes of regeneration” to produce “enough highly functional cells and tissues from one adult organ to treat thousands of patients.”

The company’s technology uses donated adult human tissue. Charles J. Queenan III, executive vice president of the company, said last week that the company had been unaware of any threats against it or any reason to believe the company would be targeted.

Police searched Karger’s home in Framingham on Friday, according to Watertown police.

Karger is awaiting trial on charges that he attempted to cause a gas explosion in the same building a year and a half ago. Karger allegedly opened three gas valves in the microbiology laboratory of Vicam, a company on the third floor the same building where the pipe bomb went off last Thursday, then lit a Bunsen burner and fled. Karger worked at Vicam at the time.

In that incident, there was no explosion because a Vicam employee came to work the next morning noticed the gas smell and called police. After police questioned Karger, he eventually confessed, The Boston Globe reported.

Karger and his attorney, Kevin Reddington of Brockton, are trying to suppress the confession, according to court records.

Karger had been on an electronic monitoring bracelet while awaiting trial in Middlesex Superior Court in October, but court records show that a judge ordered it removed last month after he posted $5,000 cash bail.

Police asked anyone with information regarding about Karger’s whereabouts to call Watertown Police or State Police.

AP-ES-08-31-04 2006EDT