Nov. 8--Editor's note: This is the first of a two-day series examining the explosion that leveled the Branch Inn, leaving one dead, many injured and Pueblo's Historic Union Avenue District forever changed. Friday marks the one-year anniversary of the tragedy.

What caused the Branch Inn to explode on Nov. 13, killing a young clerk in an adjoining store, seriously injuring others and strewing Union Avenue with broken glass and rubble?

There is a small stack of legal claims in the Pueblo city attorney's office, starting with the estate of the young woman killed, Ashley Johnson, that argues the city was negligent in not investigating reports of suspicious odors around the restaurant prior to the explosion.

Another clerk in A Classic Boutique, where Johnson was killed, was also injured, and she has filed a claim for damages against the city.

There are multiple claims from the restaurant owners that city crews damaged a buried Xcel Energy natural gas line, causing the leak that allowed gas to seep into the

basement of the Branch Inn, where the gas eventually exploded.

And there is a May 12 legal notice from Public Service Company of Colorado, which owns Xcel, alleging all of the above and serving notice that it will also hold the city responsible for claims against the utility related to the explosion.

"The notice speaks for itself," said Joe Fuentes, an Xcel spokesman.

The city, in turn, points the finger at Xcel and says the gas company is responsible for the leaking gas line. Pueblo has a franchise agreement with the utility that says the company will indemnify the city for any damages from its operations.

"City crews did not do any excavating around that gas line," said Tom Florczak, deputy city attorney, during a recent interview about the claims in the city.

And that's where the matter sits, almost one year after the explosion.

The mechanics of what happened at the Branch Inn on that tragic afternoon are known.

A little after 2 p.m. on that sunny Thursday, an explosion in the basement of the Branch Inn shattered the building and caved in the adjoining boutique. Windows in nearby buildings were blown out, and cars damaged. Emergency workers found injured people in the street and in the rubble of both buildings, as well as Ashley Johnson's body.

The next day, investigators from the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives, along with Pueblo police, firefighters and investigators from Xcel began a four-day process of methodically taking apart the collapsed buildings, looking for the source of the explosion.