Kent Police was called to the B2075 Romney Road at 6.20pm on Sunday 18 April 2021 after the incident involving a black Dacia Duster Ambiance and a white BMW M135i.
The driver of the Dacia, a woman in her 50s, and two male passengers in the BMW, one in his 20s and another in his 40s, were all pronounced dead at the scene.
The driver of the BMW, a man in his 30s, was airlifted to a London hospital where he continues to receive treatment for serious injuries
Officers from the Serious Collision Investigation Unit are appealing for witnesses to come forward and are particularly keen to hear from six people who were stood together on a grass verge north of Lydd Golf Club, a few hundred metres from where the collision occurred, or anyone who was walking along Romney Road between 6pm and 6.30pm.
They also remain keen to hear from anyone who may have dashcam or CCTV footage that may assist them.