PORTLAND, Ore. -- Investigators continued to look for whoever was responsible for blowing up a pipe bomb in Southeast Portland last month so loud it was heard for miles.

The large pipe bomb was embedded in the hill at Powers Marine Park, near the Sellwood Bridge, on the west side of river when it went off on March 28. Low clouds trapped the sound in, and caused it to bounce across city.

Most of the reports were clustered in Southeast Portland. Twitter and Facebook users also buzzed about it and officers said they were able to zero in on the location of the pipe bomb with the help of online social media.

Audio:9-1-1 calls about explosion

Portland Fire Bureau investigators said Thursday they were looking for any information on any vehicles, boats, or people in or near the park before or after the explosions.

The boom was so powerful it even set off car alarms near the Sellwood Bridge.

Investigators also asked that in the event of another explosion people be extra vigilant in reporting any nearby activity.

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