Speaking to the Evening Standard, Zeba Begun, whose house overlooks the scene where the woman died said:
"She then looked to her left and then to her right and I had no idea what she was going to do, I thought maybe she was joking about, but then about 30 seconds later I heard some beeps from the oncoming traffic which could see her.
"And she just waved at the traffic and then fell down onto the road. As soon as I saw it I called the ambulance and police."
More top news
The 14-year-old vanished near her home in west London exactly three weeks ago.
A Labour MP tipped as a possible candidate for London mayor has admitted crashing into a motorcylist her second accident in just over a year
The 48-year-old man was held on suspicion of theft from heritage and protected sites.