A man accused of kidnapping, drugging and sexually assaulting a nine-year-old girl denied putting Benadryl in her drink, and said his goal was to keep her “safe”, a court heard.

American pilot Robert Prussak approached the girl outside Harrods, who was lost after becoming separated from her family during a trip to London from France, on April 22 this year, Isleworth Crown Court heard.

She was standing outside Harrods and it is alleged that Prussak walked the girl to his flat, gave her bitter-tasting water, and that she felt tired after drinking it.

The 57-year-old, of no fixed address, then allegedly took her to a nearby park where he sexually assaulted her.

On Friday, Prussak said he was walking past Harrods on his way to Buckingham Palace when he saw the girl, and at first thought she was “waiting for somebody” and decided to continue walking, but then thought she might need help as she appeared to be “looking around, searching”.

He told the jury: “My mind went straight to my own daughters who are just a few years older than her and I thought if my daughters were lost in a big city, I wouldn’t want them stuck out alone. I was reluctant to get involved.”

Prussak spoke to the girl and she answered in another language so he started communicating with her using the Google Translate app, he said.

The defendant said he asked the girl how long it had been since she saw her parents and she raised three fingers, which he said he took to mean three minutes.

He said he asked if they were going shopping “to see if we could rush in there (Harrods), her answer was no, and then I said, well then where were you going? She wrote down something in translation, ‘muse'”.

Prussak said he came to understand that meant “museum”, but added she did not know which one.

Asked why he did not stay with the girl outside Harrods, he said: “In honesty, knowing everything I know now, that they were inside Harrods, staying there or going inside would’ve been the best solution.”

Prussak said he started walking with the girl towards a museum to “hopefully intercept the parents” and searched on his phone for police stations and “surprisingly they were fairly far”.

He said his intention was “to get her back with her parents”.

The accused said his goal was “keeping on track to a museum and keeping her safe and comfortable”.

Asked why they did not go to the museum, he said it started to rain more heavily and they had not seen the girl’s parents. He said his apartment was “very close by” and he knew “how to get there quickly”.

He said he “absolutely regrets” not calling the police sooner. And he did not call as he did not know “what response I would get” and was afraid “they’d send the cavalry and ambulance and everything”.

Prussak decided to take the girl back to his apartment and said he then searched for emergency services online, the offered her water and she drank two glasses, one from the kitchen tap and one from a bottle.

He then said through the translation, the girl used the word “bite”, and a few discussions later he “figured” she meant “bitter”, then tested his own water from the same bottle and said it tasted “normal”.

Catherine Donnelly, defending, put to him the allegation that he put Benadryl in the water, and asked him if he did that, he responded “no”.

She then asked: “The allegation is you did that to put her to sleep or stupefy her or something of that nature, did you do that?”

Prussak responded: “No.”

He was then asked if he was aware how long they had been at his apartment. He said after he left he thought it was “about an hour”, but later found out it was two hours, which “surprised” him.

The court previously heard the girl was later taken to hospital, where she was reunited with her family, and a urine sample was collected from her.

The sample contained diphenhydramine, the active ingredient in Benadryl, an antihistamine which typically causes drowsiness, the court heard.

Nneka Akudolu KC, prosecuting, reading out agreed facts on Friday, said glasses that contained a clear liquid were seized from the kitchen and the liquid was tested for Benadryl, and the results were all negative.

Dr Paul Skett, a pharmacology expert, told the jury on Friday morning that Benadryl is used as both a “sleeping pill to aid sleep and also to aid in the treatment of allergic reactions”.

Prussak told the jury he joined the air force in 1997 as a scientist then later trained to become a pilot and stayed in the military for about 18 years.

He denies three counts of sexual assault of a child under the age of 13. He also denies one count of kidnapping, one count of committing an offence of kidnapping with an intent to commit a sexual offence, and one count of administering a substance with intent.

The trial continues.