Get 3d coordinates from 2d point

function onDocumentMouseDown( event ) {
   event.preventDefault();
   mouse2d.x = ( event.clientX / window.innerWidth ) * 2 - 1;
   mouse2d.y = - ( event.clientY  / window.innerHeight ) * 2 + 1;
   mouse2d.z = 1;

   var r = new THREE.Ray();
   r.origin.copy( mouse2d );
   var matrix = camera.matrixWorld.clone();
   matrix.multiplySelf( THREE.Matrix4.makeInvert( camera.projectionMatrix ) );
   matrix.multiplyVector3( r.origin );
   r.direction = r.origin.clone().subSelf( camera.position );
   var c = THREE.Collisions.rayCastNearest( r );
   if( c ) {
//////////////////HERE GET THE 3D POINT COORDINATES////////////////////////
      c.mesh.materials[ 0 ].color.setHex( 0xaa0000 );
   } else {
      plane.materials[0].color.setHex( 0xF9EFD7 );
   }
};