THIS is Alexander Pacteau buying bottles of caustic soda at a city shop less than 10 hours after he murdered Karen Buckley.

CCTV footage shows the 21-year-old calmly loading up his basket and paying for the bottles, which he would then use to try and dissolve Karen's body.

Karen was murdered by Pacteau in Kelvin Way, in Glasgow's West End, at around 1.10am on Sunday April 12.

He repeatedly clubbed her on the head with a spanner and throttled her before attempting to dissolve her body in a bath of corrosive caustic soda.

CCTV footage reveals the pair met for the first time in Dumbarton Road, after they had left the Sanctuary Nightclub, and both got into Pacteau's Ford car.

Within 20 minutes of the chance meeting, Karen was dead.

He dumped her handbag in Dawsholm Park before taking her body back to his flat in Dorchester Avenue.

The security footage shows Pacteau buying several bottles of caustic soda at the PoundStretcher store in Crow Road at around 11am the same day.

Having used his mobile phone to search the internet for information about caustic soda, Pacteau spent that Sunday morning driving to various supermarkets and DIY stores in the West End to pick up supplies for his plan.

While his flatmate is out, Pacteau carries Karen's beaten body into his bathroom and places her in the bath.

He submerges her body in caustic soda, while he tries to clean the flat of any trace of the 24-year-old Irish nurse.

At around lunchtime, Karen's worried friends report her missing and a massive police operation is launched.

As part of the missing persons inquiry, police check CCTV inside Sanctuary and outside in Dumbarton Road to try and track down the mystery man Karen is spotted with.

Her handbag, which was found by a member of the public, was handed it into officers and concerns about her welfare continue to grow.

Meanwhile, Pacteau's flatmate is due to return home, forcing the killer to drain the bath and wrap Karen's body in a duvet overnight in a bid to keep his secret.

Sources close to the probe said at around 4.50am on Monday April 13, Pacteau goes to the Forth and Clyde Canal and throws the blood-stained spanner into the water.

He then drives to a 24 hour supermarket and asks a shop assistant to recommend a cleaning agent for removing blood from a mattress.

After spending more than an hour trying to clean Karen's blood from the duvet and mattress, Pacteau decides to burn everything she had come into contact with.

Later, he buys a 220-litre blue plastic barrel and, before placing Karen's body inside, he fills it with more caustic soda.

That afternoon, Pacteau takes the barrel to High Craigton Farm, near Milngavie, where he used to store fireworks.

He agrees a deal with the farmer to rent an outhouse for £10 for a week and hides the barrel inside.

Pacteau then places a cotton sheet, paper shredder and bicycle wheel on top of the barrel.

In another attempt to get rid of all traces of Karen, Pacteau takes his car to the Anniesland Valet Centre and gets it cleaned inside and out.

Within moments of him arriving home, police - who have now identified Pacteau as the unknown man seen with Karen - chap the door of his flat in Dorchester Avenue.

Pacteau answers and says to the officers: "I was just coming to see you."

A source close to the investigation said: "As soon as he opened the front door, the officers were hit by an overwhelming smell of bleach.

"It immediately raised alarm bells.

"Pacteau admitted that Karen was in his flat, he said they had consensual sex and she left - alive and well - at 4am."

He agreed to go to Helen Street Police Office to give a witness statement.

The source added: "He said they went back to his flat, drank alcohol and had consensual sex.

"He then said that during intercourse, Karen fell off the bed. He claimed he hadn't realised she had been bleeding until the morning.

"Then he admitted he had got rid of some stuff from his flat and burned it. He said he panicked when he heard Karen was missing."

Police didn't have enough to hold Pacteau and he was allowed to leave the station late that Monday night.

Officers put him up in a hotel while they carried out investigations and held a press conference to try and get information from the public about Karen and the movements of a grey/silver car.

On Wednesday April 15, police decided they had enough evidence to treat the courier firm owner as a suspect.

He was detained in Starbucks in Nelson Mandela Place in Glasgow city centre shortly before 2pm and, again, was taken to Helen Street Police Office.

Pacteau was searched upon arrive and officers found a handwritten note, on hotel-headed paper, which detailed the version of events he had earlier given to police.

Our insider added: "He was obviously losing track of this lies."

Around an hour later, a member of the public contacts police with information about High Craigton Farm.

He explains how he worked with Pacteau when they sold fireworks together and they used to store their goods at a farm near Milngavie.

This vital tip-off led police to the farm - and ultimately to Karen's body.

Five hours after they arrived at High Craigton and safety tests were carried out by toxic substance specialist, detectives were cleared to open the barrel.

Inside was Karen's body. Her head wrapped in parcel tape and her naked body submerged in caustic soda.

Police said a post-mortem examination revealed Karen had been hit 12 or 13 times on the head with a spanner and violently strangled.

It also showed a series of bruises on her hands and arms that were consistent with a struggle.

Karen had fought for her life.

Her family are understood to take comfort in knowing that their daughter "fought back".

Despite the overwhelming evidence, Pacteau continued to lie.

"He changed his story", the source added.

"Now he was saying that during sex, Karen slipped and hit her head, making her very angry.

"He said she was repeatedly slapping him and he reached out for the first thing he could find - which was a spanner - and hit her on the head.

"He said she died at 5am.

"But this was all lies.

"He admits throwing the spanner in the canal, burning the mattress and Karen's clothes, as well as disposing of her body in caustic soda.

"After this, he was charged."

Pacteau eventually came clean about his crime, which had shocked Glasgow.

His victim, a qualified nurse, had come to the city to study occupational therapy at Glasgow Caledonian University and further her career.

She had spent six happy weeks in Glasgow before her life was brutally snatched away.

Karen and Pacteau had both been enjoying a night out with separate groups of pals on April 11.

Police believe they had never met before, not even inside Sanctuary that night.

It was a chance meeting with "drunk" Pacteau in the early hours of the morning that led to Karen's death.

Despite his "elaborate plan" to dispose of Karen's body, the forensic evidence was damning.

Tiny blood spots were found in his car, bedroom and bathroom. He even left a fingerprint inside the barrel used to hide the body.

In the end, the evidence was overwhelming and Pacteau plead guilty.

But his confession had not saved her family from hearing the gruesome details of her death or the pain of a life without their beloved daughter.