John, a student, had a bad fight with his girlfriend, Gail. They agreed to split up. Prior to that, Gail was living with John in his apartment and had her own key. When John left for class, Gail immediately went to the police and reported that John was selling drugs in his apartment. She said she was John's girlfriend and was living in the apartment with him. Without obtaining a warrant, the police went to the apartment and asked Gail to open the door and let them in. She did, and the police found heroin, which they seized. Was the seizure valid? State your reasons.

del Carmen, Rolando V.; Hemmens, Craig. Criminal Procedure: Law and Practice (p. 224). Cengage Learning. Kindle Edition.