ISTANBUL — Turkish police are investigating after a vacationing family of four died of suspected poisoning in Istanbul.

The Böcek family, who were visiting from Hamburg, Germany, fell ill on November 12 after a day touring one of Istanbul’s main tourist spots and eating street food, according to Turkish state-run news agency Anadolu.

Initially treated for what appeared to be food poisoning, the family was discharged from a hospital but returned later with worsening symptoms.

The two children, Kadir, 6, and Masal, 3, died Thursday, and their mother, Cigdem, 27, died a day later. The father, Servet, 38, remained in critical condition over the weekend and died on Monday, Anadolu reported.

Authorities initially considered food poisoning as the cause of death and swept up street food vendors from Istanbul’s lively Ortaköy area.

But investigators shifted their focus to pesticide poisoning when two more tourists staying at the same hotel as the Böcek family were hospitalized on Saturday. Turkish media reported that a product used to kill bedbugs was sprayed in a ground-floor room and may have reached the family’s room through the hotel’s ventilation system.

The hotel in Istanbul’s old city has been shuttered by municipality officials pending the outcome of the investigation. Forensic teams flooded the hotel on Saturday, collecting samples from bedsheets, pillows, water bottles and blankets, according to Anadolu.

A preliminary forensic report said further analysis is needed for concrete answers but that an environmental toxin is the more likely culprit, Anadolu reported.

“Considering how the incident occurred, their medical history, the latest information obtained, and the fact that two other people from the same hotel were hospitalized with similar complaints, it is believed that the mother, father and children most likely died as a result of chemical poisoning caused by the environment of the hotel where they were staying, and less likely due to food poisoning related to what they had consumed,” the report said, according to Anadolu.

Seven of the 11 suspects detained by Turkish police have been taken to Istanbul’s main courthouse and are awaiting further processing.

The family has been buried in their ancestral town of Bolvadin in central Turkey. While receiving mourners paying their respects, Cigdem’s father, Mehmet Celik, told Turkish media that his daughter had recently finished renovating their summer house with hopes of one day living there.

“They died without ever being able to sleep in it,” he said. — CNN