By Nick Watt, Jason Hanna and Jason Morris, CNN

(CNN) -- Sean Philips had just woken up and was sitting on his couch when he heard the blast that would take his neighbor's life.

The explosion, police now say, came from a package that Anthony Stephan House encountered on his front porch in north Austin on the morning of March 2.

Police say it was the first of three mysterious package bombings in 10 days in Texas' capital -- explosions that have killed two people, including House, injured two others and left city residents on edge and highly suspicious of packages delivered to their homes.

Philips said he was waiting for his children to get ready for the day when he heard something like "an empty trash dumpster getting hit by a truck" around 6:50 a.m.

"I ran outside and I saw him standing over there" in front of his house, covered in blood with his clothing torn up, Philips told CNN on Tuesday morning. "He was glazed over, and .... wasn't responding to seeing me or hearing me, or anything.

"He collapsed. I gave him two rescue breaths to get him breathing again, and called 911, and did what they told me."

Medics arrived after another neighbor helped roll House over. House, 39, would die of his injuries.

"It's been the most traumatic thing in my life," Philips said.

This package, and two more that exploded at other Austin residences 10 days later, were placed in front of houses, Austin Police Chief Brian Manley said. All were average-sized delivery boxes, and they weren't delivered by the US Postal Service or delivery services such as UPS or FedEx, police said.

Philips said he didn't immediately know that a package had exploded. He said he was too zoned in on his wounded neighbor to understand what had happened.

"At the time, we assumed it was a gas explosion or something completely accidental," he said.

Police said last week they thought the incident was isolated, and they didn't immediately rule it a homicide. But they consider it a homicide now, and say they believe the three explosions are related.

But they say they don't know of a motive. Philips said he doesn't know what could have prompted the bombing, either.

"Nobody saw anything strange or odd. One neighbor says her dogs bark anytime anybody walks by -- and they do -- and they didn't bark that morning at all. There's no sign or clue to what happened," he said.

Philips said he didn't know House well, but the two men were acquainted because their daughters are friends.

He said his neighborhood is "on guard."

"Everybody is real suspicious if there's any packages," he said. "But most of all we just want answers, to know what happened to our neighbor and what's happening to the other people in Austin."