The clausal complements of verba dicendi are introduced either by the serial verb bi(fi) 'say' (usually in the short form bi), by complementizer dati 'that', or by a null complementizer. The distribution of these complement types depends at least on the selecting verb, and on the nature of the complement (direct/indirect speech). As a result, it is not possible to generalize over this class of verbs in terms of the frequency of the different complement types. Occasional use of complementizer bi(fi) followed by a clause introduced by dati suggests that serial bi(fi) has the same subcategorization properties as its main verb counterpart, i.e. that it selects for a CP.
Source: Kouwenberg 1994: 333
Source: Kouwenberg 1994: 403
Source: Kouwenberg 1994: 405
Source: Kouwenberg 1994: 332