Did Boston bomber run stolen SUV over his brother?

Dzhokhar Tsarnaev, the younger of the two Chechen brothers suspected of the Boston marathon blasts, probably killed his elder brother Tamerlan by running over his SUV over him while fleeing, police said.

Dzhokhar, 19, who was arrested on Friday after days of manhunt, is in serious condition in a Boston hospital. His elder brother, Tamerlan, 26, the alleged mastermind of the Boston marathon bombing died a day earlier during a police exchange fire.

In an interview to the Boston Globe, Watertown Police Chief Ed Deveau claimed that Dzhokhar ran over his brother on his stolen SUV when the police was about to handcuff and arrest him on Thursday night after exchange of fire. His autopsy report has not come in yet.

Describing the chain of events, Deveau said after days of manhunt, a local police spotted the two brothers driving in two cars -- Honda sedan and a stolen Mercedes SUV. Soon the two brothers jumped out of their vehicles and started firing on the police, while more police were rushed to the scene.

"Quickly we had six Watertown police officers and two bad guys in a gunfight," said Deveau. At least 200 shots were fired, maybe as many as 300, he told the Boston Globe.

The shots, around 12:50 am, woke resident Jennings Aske, at 66 Laurel Ave. When he looked out his window he saw a green Honda Civic sedan stopped in the street, with its lights on and the driver's side windows blown out. A husky man -- apparently Tamerlan Tsarnaev -- stood nearby firing a gun, the daily reported.

I saw him standing there shooting at police. When he fired, there was a little flash of light. I could hear the gun firing. It was terrifying," he told the daily.

According to Deveau, the Tsarnaev brothers hurled something at the officers -- apparently a pressure cooker bomb -- and there was a tremendous explosion. Police later found the lid to a pressure cooker.

"We believe it was an exact duplicate of the Boston Marathon bombs," he said adding that the two suspects also threw five "crude grenades" at officers, three of which exploded.

After several minutes of exchange of fire, Deveau said Tamerlan apparently ran out of bullets. Police officers tackled him and were trying to get him handcuffed. It is at this point of time Dzhokhar came driving on the stolen Mercedes SUV, as a result of which the officers scattered and the SUV ploughed over Tamerlan Tsarnaev, who was dragged briefly under the car.

Dzhokhar abandoned the SUV almost immediately on a nearby street and fled on foot, triggering an all-day manhunt, Deveau said.

Meanwhile, Boston Police Chief Ed Davis said that the two suspects were not only armed, but also had explosive devices indicating that they were planning other attacks.

"I personally believe they were (behind the Boston marathon bombing). We have reason to believe, based upon the evidence that was found at that scene, the explosions, the explosive ordinance that was unexploded, and the firepower that they had, that they were going to attack other individuals. That's my belief at this point in time," Devis told CBS's Face the Nation -- a Sunday talk show.

"More than 250 rounds of expended ammunition was found at the scene. This was because of a 5 to 10 minute gun battle that occurred there, punctuated by loud explosions, as several explosive devices went off. They were homemade," he said.

"There have been published reports that the top of a pressure cooker was also found. My officers had reported to me that there was an extremely loud explosion followed by a series of smaller ones as they engaged in the gun battle with the suspect," he said.

He also said that the suspects had Improvised explosive Devices and they had homemade hand grenades that they were throwing at the officers.

"This was a heavily armed and extreme dangerous two individuals," he said, adding that unexploded devices were also found in the abandoned Mercedes SUV, besides other unexploded devices from other places. "So this was as dangerous as it gets in urban policing," he said.

"They were homemade explosives. The pressure cooker explosive has been widely talked about. There is not only explosive gun powder, but shrapnel that's put into this device. There were smaller ones that were comprised of the same type of shrapnel. So there's no doubt they were made by these two guys," Davis said, adding that there were at least four unexploded devices.

"I don't exactly know the number from Watertown. I have not got the full report on it. But I saw two or three of them on the ground and there was at least one more," he said.