Des Moines police are investigating the explosion of a pipe bomb in an apartment complex parking lot. Lieutenant Kelly Willis says the device went off about 6 this morning, no one was injured. Two other bombs have been found in the last six weeks, one along aDes Moines bike path and one attached to a car in the suburb of Urbandale. Each bomb has been found on a Tuesday and they’ve been spread out two weeks apart. Willis says they’re trying to determine if the same person made all three devices.The Federal Bureau of Alchol Tobacco and Firearms, Des Moines police and the Urbandale police department have formed a task force to work on the case. He says they’re asking for the public’s help in finding the person responsible.Willis says they’re lucky no one has been injured.The A-T-F is offering a five-thousand dollar reward for information leading to an arrest in the first bombing.