WASHINGTON (REUTERS) - Major public events in the United States like the Boston Marathon need tighter security but officials must avoid moving toward a "police state", Boston's police commissioner said on Thursday at a congressional hearing into last month's bombing.

Commissioner Edward Davis called for more use of surveillance cameras and other technology as well as special police units and more undercover officers as ways to provide more security. But the public's privacy must also be protected, he added.

"We do not, and cannot, live in a protective enclosure because of the actions of extremists who seek to disrupt our way of life," Mr Davis told lawmakers probing the April 15 bombing in which three people were killed and 264 wounded.

The hearing by the House of Representatives Homeland Security Committee is the first in a series examining events leading up to the bombing that struck crowds cheering at the finish of the marquee race.

Surveillance video aided United States (US) officials in naming two ethnic Chechen brothers as responsible for the attack.

One, Dzhokhar Tsarnaev, was captured and charged in the bombing. His older brother, Tamerlan, was killed in a shootout with police.

Federal authorities have also charged three others with interfering with the investigation. The probe is continuing, with the focus now on computer evidence as well as a trickle of information coming from Russian authorities.

Lawmakers questioned the ability of law enforcement and intelligence agencies to coordinate information to prevent similar attacks.

Both Republicans and Democrats said they were concerned that systems set up after the Sept 11, 2001, attacks in New York and Washington still were not successfully sharing details about potential perpetrators.

CONNECTING THE DOTS

Lawmakers said they worried that federal officials were not sharing information with state and local law enforcement, pointing to the FBI, the CIA and the Department of Homeland Security.

"Here we are, 12 years later - why are we still having problems connecting the dots?" said Representative Michael McCaul of Texas, the committee's chairman. "My fear is that the Boston bombers may have succeeded because our system failed."

After the April 19 shootout, officials revealed that the FBI, acting on a request from Russia, interviewed Tamerlan Tsarnaev in 2011 and his details were put in a counterterrorism database. But this did not set off alarms when he flew to Russia in 2012.

"The failure to share information is absolutely indefensible," said Representative Peter King, a New York Republican. "I can't explain it, I can't understand it, and to me it's a severe breakdown in law enforcement."

The FBI said Boston police officials had access to their records on Tsarnaev, and the roughly 1,000 other people assessed by the Boston joint terrorism task force in 2011, through an online database set up in 2004.

"Many state and local departments, including the BPD, have representatives who are full-time members of the JTTF, and specifically had representatives assigned to the JTTF squad that conducted the 2011 Assessment of deceased terrorism suspect, Tamerlan Tsarnaev," said Mr Richard DesLauriers, the FBI's special agent in charge in Boston.

Mr Davis told lawmakers that surveillance images can be helpful to law enforcement as evidence and are aimed at protecting the public, not stifling freedom or chilling free speech.

Still, he added: "I do not endorse actions that move Boston and our nation into a police state mentality, with surveillance cameras attached to every light pole in the city."

Mr Davis and others said that even with more coordination among law enforcement, databases and cameras can only do so much to prevent such attacks.