New York City Police Commissioner Ray Kelly, who joined Bloomberg at a news conference this morning, said that the bomb was a "low-order explosive" made with powder placed in a green ammunition box.
"It was not a particularly sophisticated device," he said.
After the release of the video, Kelly said it was not clear if the grainy, poor quality video could be enhanced but added that investigators were still checking other video cameras in the area and hoped to find a better images.
No other eyewitnesses to the explosion have emerged, despite the fact that the recruiting station is directly across the street from a police substation and right in the middle of the famed "crossroads of the world."
The lone officer in the station heard the explosion and ran outside, Kelly said, but saw nothing. He did encounter a man who said he saw a man on a bicycle wearing a hoodie, dark clothing and a backpack acting suspiciously near the installation around the time of the blast.
The witness did not see anyone actually place the device or see the explosion, Kelly said.
Both the mayor and police commissioner emphasized that they had no evidence of any outside terrorist connection. There is "no evidence of any connection to anyone else," Bloomberg said.
The FBI is investigating the incident, along with the Joint Terrorism Task Force, which is made up primarily of FBI and New York Police Department officials. Any prosecution would likely draw federal charges since a military installation was targeted.
Tourists staying at a Marriott hotel four blocks away told The Associated Press they heard, and felt, the blast.
"It shook the building. I thought it could have been thunder, but I looked down and there was a massive plume of smoke, so I knew it was an explosion," said Terry Leighton, 48, of London, who was staying on the 21st floor of the Marriott.
Bloomberg, talking to reporters in a hectic Times Square, assured tourists and residents this morning, hours after the explosion, that the city was safe.
"New York City is open for business," he said.
Early in the investigation, subway cars passed through the Times Square station without stopping, but normal service was restored, with some delays, before the morning rush hour began.
The recruiting station, located on a traffic island surrounded by Broadway theaters and chain restaurants, has occasionally been the site of anti-war demonstrations, ranging from silent vigils to loud rallies.
"If it is something that's directed toward American troops that's something that's taken very seriously and is pretty unfortunate," Army Capt. Charlie Jaquillard, commander of Army recruiting in Manhattan, told the AP.
Although officals said they had no evidence to connect today's incident to earlier, similar incidents, the attack on the recruiting station did bear strong similarities to two past explosions in which small homemade bombs or incendiary devices were tossed at official buildings in New York City. Two were tossed at the British consulate in 2005 and two were tossed at the Mexican consulate last October.
In each case, a man on a bike was captured in hazy video images. Police found no second device this time.