The ITV show centred on the death of Alice Ruggles in October 2016 and showed the moments between her body being discovered to the killer being charged.
The shocking programme gave viewers an insight into how the police use “The Golden Hour” after being alerted to the murder in order to catch the culprit.
Tonight’s documentary showed Alice’s final moments alongside the police investigation and heartbreaking interview footage with her grieving parents.
Viewers were left in tears watching the ground-breaking episode, and flooded to Twitter to discuss the complex case.
One posted: “Fascinating insight into police procedure. Such an upsetting case. Heart goes out to the family.”
Another added: “Absolutely devastating what happened to Alice, seemed like such a lovely girl. Lots of respect to the family/police.”
A third commented: “#AnHourToCatchAKiller is so harrowing to watch the way she was sending text messages & within 25 minutes was gone.”
A fourth agreed, tweeting: “I have no words, absolutely heartbreaking.”
Lance Corporal Trimaan “Harry” Dhillon was found guilty of Alice’s murder and was imprisoned for life with a minimum of 22 years.
The show uncovered how he climbed through his ex-lover’s window and slashed her throat after being rejected.