Tikka was a member of several law preparation work groups, and had a central influence in the development of Finnish taxation law. Among his achievements are the system for refunding corporate tax, which was later abandoned, as taxing Finnish and foreign dividends differently became contrary to the European Union basic treaty.
Before his death, Tikka publicly announced his support for the flat tax. He proposed that different taxation of capital income and work income widens the financial gap between corporate shareholders and regular workers.
Kari S. Tikka wrote several scientific articles and books, among which are "Veropolitiikka" ("taxation policy") and "Yritysverotus I-II" ("corporate taxation I-II"), together with O. Nykänen. His PhD thesis "Veron minimoinnista" ("on the minimisation of tax") was at its time one of Finland's best selling PhD theses.
The Helsinki police arrested two men suspected of the killing, a 19-old Russian Aleksandr Ionin and a 23-year-old Estonian Mika-Martti Zukov, on May 29. According to the police the homicide had nothing to do with Tikka's profession. The motive was robbery. In court Ionin and Zukov admitted that they had stolen 15 bottles of alcohol, 49 packs of cigarettes, a mobile phone cover, a pocket knife, one pair of binoculars, a video camera, and some cash.
The trial started on September 26, 2006, in Helsinki District Court. Prosecutor Harri Ilander demanded a life imprisonment for Ionin and Zukov for murder and an aggravated mugging. Ionin and Zukov pleaded guilty on charges of manslaughter.
Prosecutor Ilander expressed his disappointment in the sentence, but made no decision on appealing against the verdict to the Court of appeal.
His sexuality was sort of a public secret in Helsinki, as he did not conceal his frequenting in gay nightclubs, but the subject never came up in press or interviews. After Tikka's death, his homosexuality was however mentioned in stories about him.