Meaning of past form + たる

Question

In the third episode of Dantalian no Shoka I found this sentence, in which the character is speaking about the culprit in a novel; Hugh is checking a book in a bookstore, the other character is trying to get his attention:

Dalian: ヒューイ

Hugh: うん

Dalian: ヒューイ

Hugh: うんちょっと待って

Dalian: 被害者の夫です

Hugh: えっ

Dalian: 完璧なアリバイのある被害者の夫が犯人なのです。パリとロンドンを往復したたるがいくつあるのか考えればアリバイは崩れるのです

In the sub this is translated as:

The alibi falls apart, however, once you consider the accounts‌ concerning his travels between Paris and London.‌

I don't understand that たる: I found different answers about たる forms (like this, this and this), but they are relative to stem + たる, past + る and noun + たる, while here is past + たる.

I tried looking in my grammars and on online dictionaries, but I didn't find it, and while I can understand the gist of the sentence ("If you think about how many round trips he did between Paris and London, his alibi breaks apart"), I'm not sure what that たる adds, and how would the sentence be different if I were to say something like パリとロンドンを往復したのがいくつあるのか考えればアリバイは崩れるのです.

Answer 1

This たる is 樽, a simple noun meaning "barrel; cask".

パリとロンドンを往復したたるがいくつあるのか考えればアリバイは崩れるのです

The alibi falls apart once you consider the number of casks that traveled between Paris and London!

This odd sentence seems to be a reference to The Cask by Freeman Wills Crofts, one of the earliest detective novels that featured alibi breaking. According to this page and reviews here, the number of casks that traveled between Paris and London was the key to solve the mystery.

I did not know The Cask, but it was at least possible to notice this is 樽, because たる as an auxiliary cannot follow a past form. ダンタリアンの書架 seems to be set in the UK in 1919-1920, and The Cask was written in 1920, so this might have been a valid joke in those days...