Just before he got off the crowded No. 30 bus, Richard Jones noticed a fellow passenger fiddling anxiously with a bag. There was a bloodcurdling scream, and within seconds the bus exploded.

"This young guy kept diving into this bag or whatever he had in front of his feet," Jones, 61, told The Associated Press on Tuesday.

"It was like he was taking a couple of grapes off a bunch of grapes, both hands were in the bag. He must have done that at least every minute if not every 30 seconds. He was getting annoyed. The only reason I noticed it was that he was annoying me."

Jones, a computer consultant from Bracknell, west of London, said he wasn't sure if what he saw was significant — if the man was the bomber — but that he reported it to police anyway. He described the man as being about 6 feet tall, olive-skinned and clean-shaven, wearing light brown trousers and a light brown top.

Police are investigating the possibility that the four men who attacked the double-decker bus and three London subways July 7 were homicide bombers. Personal property belonging to one suspect, believed to be from West Yorkshire, in northern England, was found in bus wreckage. That man's family called police to report him missing about 12 hours after the explosion, police said.

The crowded No. 30 bus was stuck in morning rush-hour traffic in Tavistock Square (search), in the famously literary Bloomsbury neighborhood. Jones decided to join another passenger who said he was going to walk instead.

"We banged the back of the bus and the driver then let us off," he said, adding that between 12 and 20 other people joined them. "Immediately, bang! There was an explosion behind me, and I turned round and said, 'I can't believe it, I just got off that bus."'

"What I did hear just before the explosion was an excruciating scream ... a crazy scream," he said. He could not tell whether the voice was male or female.

The bus blew up at 9:47 a.m. Thursday, killing 13 people. It was about a mile from King's Cross (search) station, where police said the four suspects were seen on closed-circuit television just before 8:30 a.m.

A woman on the street asked Jones if he had just gotten off the destroyed bus. When Jones said yes, "she actually knelt down in front of me and prayed," he recalled.

Still, he said he wasn't too shaken by the experience.

"I felt a huge adrenaline rush and then I quickly rationalized it to very much like stepping off the pavement and almost getting run down by a car, and then stepping back on the pavement and life goes on."