On the morning of April 22, 1997, a Tuesday, McGrath and his partner, Detective Raymond Krakausky, began a stakeout in an alley near Urdiales' parents' home, where Urdiales had resided following his discharge from the Marine Corps years earlier. It was a working-class neighborhood where unassuming bungalows and duplexes line the streets, and where the murder suspect's parents had lived for more than 10 years. As luck would have it, McGrath and Krakausky did not have to wait very long. Urdiales came out at approximately 9 a.m., leaving for his job as a security guard at a downtown Chicago Eddie Bauer store. The two detectives walked up to Urdiales and told him that they needed to speak with him about the incident in November 1996 in which his gun had been confiscated. Urdiales politely told them that the case had been resolved, but the detectives insisted there was unfinished business regarding the .38-caliber revolver. After minimal hesitation, he agreed to accompany the two detectives to their offices.
At one point McGrath asked Urdiales where he had obtained the gun, and he told him that he had purchased it about five years earlier in Calumet City for $300. When asked if it had ever been out of his possession, he said that it had not and stated that it had been under his exclusive control until it had been confiscated by Hammond police officers. At another point during the questioning, McGrath indicated that he and his partner were investigating some unsolved crimes, shooting deaths to be precise, involving a .38-caliber gun, and showed him photos of Uylaki, Corum and Huber. At first Urdiales said that he did not recognize the three women, but when McGrath told him that the bullets used in their murders matched his gun, he paused for a moment and then responded that he guessed he would not be going to work that day. He took off his security badge, loosened his tie, and began untying his shoe laces. He then provided the detectives with details of his murders of Uylaki, Corum, and Huber. Without any additional prompting from the police, Urdiales also said that there were "some matters" that police in California "might be interested in." Up until that point, police in neither state had connected the earlier murders in California to those in Illinois.