BOSTON — A man charged with leaving an explosive device next to a Boston police cruiser has been held on $750,000 bail, but an attorney says the suspect is the victim of a "witch hunt" who's been framed by unreliable witnesses.

Pleas of not guilty were entered on behalf of 42-year-old Asim Kieta at his arraignment Monday on charges including possession of an explosive device and assault with intent to murder.

The improvised bomb that included a propane tank exploded Friday morning outside a police substation in South Boston. Two officers suffered minor injuries.

Kieta's attorney questioned whether a bomb was involved, saying some trash caught fire.

Police have not disclosed a motive but say the suspect was spotted on surveillance video. He was arrested Saturday at his job as a cook.