"We do not know how many more devices might be out there."
MAINZ, Germany — A vengeful landscape gardener planted bombs targeting people he was embroiled in disputes with before being found dead, according to police in Germany.
Investigators are hunting for more devices after two booby-trapped logs were discovered, including one at a home owned by an American that is also inhabited by a U.S. family.
Bernhard Graumann, 59, is also suspected of leaving a bomb outside an office in Enkendorf-Alsenborn. A 64-year old doctor was killed by that device on Friday — just hours after Graumann's body was located. Police believe Graumann died by suicide or from natural causes.
Two days later, a log that had been rigged with explosives detonated in a stove, injuring a 34-year old woman and her 4-year old daughter.
Another booby-trapped log was found Wednesday in a carport outside a house in Fischbach. Its owner "is an American woman, who apparently had a troubled business relationship with Graumann," police spokesman Bernhard Christian Erfort told NBC News.
An American family who rents the residence was not at home when it was destroyed by a bomb disposal team.
"Our experts say that the explosives could have severely harmed or even killed people," Erfort said.
Investigators found "gunpowder and other devices banned under Germany's explosives act" during a search of Graumann's home.
Police warnedthat "people who had problematic private or business relations with Graumann" should get in touch as soon as possible.
"We do not know how many more devices might be out there," Erfort added.