AUSTIN, Texas -- Austin police say they are dealing with a highly sophisticated bomber who is more skilled than they first believed.
Another bomb went off in Austin Sunday night injuring two men. "I heard a boom, a huge explosion," said Eliza May who lives near the bomb site.
Police say the bomb was not on a porch like the other three bombs but near a fence. Police believe the bomber used a trip wire to set it off.
May provided WFAA with these pictures from her backyard. She's been on lockdown most of the day, but talked to WFAA by phone. "This was a random victim, not a targeted home," said May.
Police say the bomb was most likely placed near a fence and believe a bicyclist may have tripped the wire.
"There were a lot of nails in the bomb, so the victim's legs were injured, punctured," said May.
Police say the bomb contained the same material as the other three bombs, so they say it's connected. The use of a trip wire takes the investigation to a new level.
"We are dealing with someone with more skill and sophistication than we first believed," said Austin Chief Brian Manley.
The victims in the other three cases were minorities in this case -- they are two white men in their 20s. The bombing is on the other side of Austin from the others.
"I think it's going to heighten people's concerns because of the randomness of this," said Thad Holt.
More than 500 federal agents have been called in to help and more are on the way. And DPS troopers are helping Austin police patrol the streets.
In this case, they may have some surveillance video. They hope will give them some clues and lead them to a possible suspect before he strikes again.
Chief Manley said that San Antonio and Houston Police Departments are sending officers to help patrol..