Sini also said that police are investigating whether gang MS-13 were behind the murders.
Police have not commented on the alleged phone call.
Police say the four were killed in a manner consistent with victims of the MS-13 street gang.
Prosecutors said Kayla Cuevas, 16, was targeted last summer by a group of four gang members because she had been feuding with MS-13 members at school and on social media.
Police say the bodies of four apparent homicide victims have been found in a Long Island park.
"It appears they were killed with a sharper-edged instrument", Sini said.
Sini said police are not ruling out any possibilities in the investigation. It's all hands on deck until we solve these murders'. The victims were identified by family members as 16-year-old Justin Llivicura, cousins Michael Banegas and Jefferson Villalobos, both 18, and Jorge Tigre.
"They'll kill anybody", said Isaiah Vogelfang, whose own brother, Michael Johnson, was allegedly killed by MS-13 members previous year.
Jorge Tigre, of Bellport, had been reported missing to Suffolk police at 3:28 p.m. Wednesday and police began searching for him at 3:36 p.m., police said Thursday. 'This is a long-term war and make no mistake about it - it's a war.
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The bodies were found in a park bordered by Clayton Street and Lowell Avenue, ten minutes drive from the center of Brentwood.
"He kept his distance from them", his sister Monica, 20, told the Daily News as their mother wept Friday inside their home. The teens, who were best friends, were killed by "swinging baseball bats and machetes" in a suspected revenge attack.
'He called me, the friend in MS-13, he called me last night at 6:30 and told me my brother is here, ' William said on Thursday.
Tigre said he spoke to investigators at the scene, but he did not get any information from them.
The discovery comes several weeks after eight MS-13 gang members were arrested in connection with the beating deaths of two teenage girls. Pena-Hernandez was reportedly murdered for violating the gang's protocol.
It is not clear when or how the bodies were dumped in a wooded area.
Sini said the the department, in partnership with Suffolk County Crime Stoppers, is posting a $25,000 "fast cash reward" for any information that leads to the arrest of the perpetrator or perpetrators of the murders.
Authorities are yet to reveal whether the bodies discovered on Wednesday are linked to the previous youths' deaths.