A board of inquiry was formed the day of the disaster headed by H.F Anderson, Division Superintendent, Southern Pacific Railroad. The committee included the Vice-president of the San Antonio Traction Company, the President and Vice-president of Alamo Iron Works, a local druggist, a US Army Colonel Commanding the United States Arsenal, a Field Artillery Lieutenant, and seven railroadmen, five of whom were senior technicians from systems other than the Southern Pacific. The composition of the committee would seem to indicate an intentional balancing of public and private interests.

While the exact selection process was not detailed in the local newspapers, the presence of senior members of the business community would indicate the involvement of municipal interests, which at this particular time in the history of San Antonio is embodied in the awesome political personage of Mayor Bryan Callaghan. The committee, both in form and membership, could have existed only as a result of mayoral fiat or at least acquiescence. The committee began to hear witnesses that evening, the hearing was public and the local press was present. The next day, the 19th of March, the public committee held hearings for more than five hours, and examined the scene.

No.704 was on track at idle between the cooper shop and the blacksmith's shop when the explosion occurred.

Allison Mayfield, Chairman of the Texas Railroad Commission arrived in San Antonio the evening of the 19th having been requested by the Southern Pacific Railroad. He was accompanied by Railroad Commissioner William D. Williams. Chairman Mayfield stayed at The Menger Hotel and Commissioner Williams at the St. Anthony. Shortly after their arrival Chairman Mayfield was called upon by a group of three men, President Thornwell Fay, President of the Southern Pacific in Texas, H. Garwood, general attorney for the Southern Pacific, and H.F. Anderson the Division Superintendent of the Southern Pacific and head of the public committee investigating the incident. All four then went to speak with Commissioner Williams. Chairman Mayfield had already sent a telegram to Judson C. Clements, Chairman of the Interstate Commerce Commission(ICC), asking that the ICC investigate the incident. The "official" investigation was, however, to be separate from the public committee’s hearings.

On the 20th the public hearings were placed on hold awaiting the arrival of John Ensign, Chief Boiler Inspector and Frank McManamy, Assistant Boiler Inspector of the ICC. Inspector Ensign arrived late on the 21st and began his investigation at the scene. At 10:00 AM on the 22nd, the "official" board of inquiry began closed hearings at the Federal District Courthouse. The public committee was never again convened.

The official board of inquiry was composed of Chief Inspector Ensign, Chairman Mayfield, Assistant Division Superintendent(Southern Pacific RR), J. E. McLean, Assistant General Manager(Southern Pacific RR), J. W. Small, and District Inspectors(Southern Pacific RR), Shirley and Dougherty. The board was assisted by Engineer R.D. Parker of the Texas Railroad Commission, E.B. Roberts, Assistant Attorney General and J. D. Walthall the Acting Attorney General of the State of Texas.

On March 25th, Chief Inspector Ensign returned to Washington, D.C. stating that his report would be submitted to the ICC. Assistant Inspector McManamy stayed in town to conduct tests on several bolts from the Locomotive No.704 that were possibly of inferior condition, if not actually broken, prior to the accident.

Division Superintendent Anderson did make one public statement on the 24th to the effect that as far as his company(Southern Pacific) and its operations was concerned it really did not matter what was concluded by Inspector Ensign or the "official" committee.7

Various other persons arrived in San Antonio during the days immediately after the disaster to investigate. The Southern Pacific Railroad had requested that the Texas Labor Statistics Commission send an inspector. Labor Statistics Commissioner J. A. Starling provided an interview to the Austin Bureau of the San Antonio Express after his personal inspection, "Speaking from forty years experience in this line of work, I am convinced beyond doubt that the occurrence was caused by tremendous boiler pressure. The engine was one of the biggest in the country, and there was not a piece of the boiler as big as that"-here Mr. Starling indicated a small bookcase in his office-"to be found after the explosion. Of course there is no telling just what the pressure was, as the steam gauge was wrecked, or whether there was the proper supply of water, but there is no question that boiler pressure was responsible for this terrible accident."8

Captain Guy M Carelton, Assistant Chief of the Bureau of Explosives of the American Railway Association arrived in San Antonio on the 22d and began his investigation the next day. He and another investigator from the same bureau also met with Chief Boiler Inspector Ensign during their investigation. Captain Carelton’s mandate for conducting his investigation or who might have requested his assistance, was never publicly stated. Carelton did make a public statement, "The main force of the explosion was steam." When questioned as to contributory causes or collateral forces, he gave no answer.9

The men out on strike also appointed a committee composed of machinists to perform their own investigation. Their findings or conclusions do not seem to have been made public.