British police have made an arrest, given details about the movements of four suspects and conducted several raids as the investigation into last Thursday's London bombings intensifies.

One man from Leeds is in custody in London. It is believed he is related to one of the suspects.

The raids came before dawn in the city of Leeds.

An army bomb disposal expert unsuits after a controlled explosion was used to get into a house in the Hyde Park area of Leeds. The house was raided on Tuesday, July 12, in connection with last week's London bombings. (Paul Barker / AFP / Getty Images)

Police broke into five houses, then later brought in army experts to blast their way into a sixth; evacuating an entire neighbourhood over concerns about explosives found inside the unoccupied building.

Then later in the day, a train station in Luton, north of London, was shut down and police began probing a car parked in the lot. A controlled explosion took place.

Police say three men took the train from Leeds, meeting a fourth at the station in Luton.

Police focused the raids to a street in the northern city of Leeds.

When the head of the Metropolitan Police's anti-terrorism branch appeared before reporters, Peter Clarke connected the events, saying police were looking into the movements of the four men, three of whom were from the Leeds area.

Clarke linked them all to last Thursday's attacks that killed at least 52 people and injured 700 more.

"We now know that all four of these men arrived in London by train, on the morning of Thursday, July 7. We have identified CCTV [closed circuit television] footage showing the four men at King's Cross station shortly before 8:30 a.m. on that morning, July 7," he said.

All the London underground explosions that morning happened on trains that travelled through King's Cross.

Clarke said one of the suspects was reported missing by his family later that morning. That man was on the bus that blew up in Tavistock square 50 minutes after the carnage on the underground.

In the bloody aftermath of the explosion of the bus, police found a gruesome clue: the detached head of a man. This, according to Israeli experts who have experience in such things, was a telling clue that he was the person closest to the explosion. Police believe he was either a willing or inadvertent suicide bomber.

But it wasn't the only clue to the killers.

"We have found personal documents bearing the names of three of those four men close to the scenes of the explosions," said Clarke.

Clarke also says it's likely at least one of the men died in the blasts, perhaps all four. But he didn't label them as suicide bombers nor did he release their names.

In the West Yorkshire region that includes Leeds, Chief Constable Colin Cramphorn urged residents to stay calm. "I know that the people of West Yorkshire will have increased concerns for themselves and their families. I also know that there are those who would seek to exploit those concerns," he said.

But the searches, the evacuations and the suggestion that the bombers came from Leeds is making some people nervous.

"It's scary, especially when you've got your kids growing up around here, and that's not nice. There's been bomb squads, police evacuating, you can't get round and it's absolutely ridiculous," said one concerned resident.

Reports say all four of the suspects are British born. But that news may not calm people's worries.

If they were suicide attacks carried out by British citizens, it may generate even more unease among those still struggling to understand what happened and why.